1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier, printer, facsimile machine and the like, more specifically, relates to a method and apparatus for image forming capable of effectively performing a predetermined sheet finishing operation.
2. Discussion of the Background
Conventionally, when an image forming apparatus such as a copier, printer, facsimile machine and the like completes production of a copy image, a sheet finishing apparatus attached to the image forming apparatus then performs a sheet finishing operation. In the sheet finishing operation, every time a recording medium having the copy image thereon is discharged to a tray for positioning and/or stapling, a rotatable elastic member disposed in a vicinity of the tray contacts the recording medium to abut the recording medium against a stopper so that the recording medium is positioned in a travel direction thereof.
A certain period of time is required to perform the stapling operation between jobs, which prevents an increase in productivity. To improve productivity, a mechanism has been provided in which a plurality of recording media or recording sheets is stored in a sheet conveying path and is conveyed at a time to a staple tray that performs a sheet stapling operation, which reduces a period of time for the stapling operation and improves productivity.
An example of background sheet finishing apparatus having the above-described mechanism that discharges the plurality of recording sheets to the staple tray includes a rotatable moving member (hereinafter, referred to as a “knock roller”) and a protruding member (hereinafter, referred to as a “hook”) mounted on a discharge belt to discharge a stack of the plurality of recording sheets to an external tray, so that the stack of the plurality of recording sheets can be positioned.
When contacting the stack of the plurality of recording sheets, the knock roller actually contacts with a last sheet that is placed on the top of the stack of the plurality of recording sheets. The plurality of recording sheets other then the last sheet accept a force to abut the plurality of recording sheets against the stopper through friction caused between the plurality of recording sheets, thereby reducing the force. When a single recording sheet is stacked, the hook is moved in a direction opposite to a sheet discharging direction, and the knock roller contacts the edge of the recording sheet, thereby stably performing a positioning operation. When a plurality of recording sheets is stacked, the knock roller contacts the edge of the recording sheets in a travel direction of the recording sheets. The knock roller, however, cannot stably position the plurality of recording sheets. That is, it is difficult to surely perform a positioning operation.
As described above, when the knock roller and the hook perform the positioning operation, the hook is used after the knock roller contacts with the stack of recording sheets, and the plurality of recording sheets fall to a staple tray.
At this time, the stack of recording sheets stays in the staple tray and is positioned with the recording sheets adhered to each other. In this case, a greater friction is caused between the recording sheets, resulting in failure such as insufficient positioning and folded sheets.
Further, when the knock roller and the hook are used for positioning, the hook contacts the edge of the recording sheet insufficiently while the knock roller is in motion. In this case, the force to necessary to abut the recording sheets against the stopper is not obtained, therefore, the knock roller and the hook cannot simultaneously contact the recording sheets. Therefore, when the knock roller and the hook are moved, certain periods of time for respective operations are needed, which makes it difficult to apply the operations for high speed processing.